1. Field of the Invention
The invention relates to a radiation-sensitive resin composition, a resist pattern-forming method, and a polymer.
2. Discussion of the Background
In the field of microprocessing represented by production of integrated circuit devices, a reduction in line width implemented by lithography has progressed in order to achieve a higher degree of integration. Therefore, use of radiation having a shorter wavelength has been extensively studied. Examples of short-wavelength radiation include a bright line spectrum of a mercury lamp (wavelength: 254 nm), far ultraviolet rays (e.g., KrF excimer laser (wavelength: 248 nm) and ArF excimer laser (wavelength: 193 nm)), X-rays (e.g., synchrotron radiation), and charged particle rays (e.g., electron beams). In particular, lithography that utilizes excimer laser light has attracted attention due to high output, high efficiency, and the like.
It has been desired for a resist used for lithography to form a fine pattern with high sensitivity, high resolution, and good reproducibility when using excimer laser. A chemically-amplified resist that includes a radiation-sensitive acid generator that generates an acid upon exposure to radiation, and exhibits improved sensitivity due to the acid has been proposed as a resist that is suitable for far ultraviolet rays (e.g., excimer laser).
A chemically-amplified resist composition that includes an acid diffusion controller has been disclosed (see Patent Documents 1 and 2, for example). The acid diffusion controller controls diffusion of an acid generated by the radiation-sensitive acid generator in the resist film, and suppresses undesirable chemical reactions in the unexposed area. The resist composition exhibits improved storage stability, and the resulting resist film exhibits improved resolution. Moreover, a change in line width of the resist pattern due to a change in post-exposure delay (PED) from exposure of radiation to heat treatment after exposure can be suppressed (i.e., the process stability can be improved).
However, it has been desired to form a finer resist pattern (e.g., a fine resist pattern having a line width of about 45 nm) in the field of microprocessing. Such a fine pattern may be formed by reducing the wavelength of the light source of the exposure system, or increasing the numerical aperture (NA) of the lens, for example. However, an expensive exposure system is required to reduce the wavelength of the light source. When increasing the numerical aperture of the lens, a decrease in depth of focus may occur even if the resolution increases since the resolution and the depth of focus have a trade-off relationship.
In recent years, liquid immersion lithography has been proposed as lithographic technology that can solve the above problem. Liquid immersion lithography provides an immersion liquid (e.g., purified water or fluorine-containing inert liquid) between the lens and the resist film (over the resist film) during exposure. According to liquid immersion lithography, since the exposure optical path (space) is filled with an immersion liquid that has a refractive index (n) higher than that of air and the like instead of air or an inert gas (e.g., nitrogen), the same effect as that achieved when reducing the wavelength of exposure light can be achieved even when the previously used exposure light is utilized. Specifically, high resolution can be obtained while preventing a decrease in depth of focus.
According to liquid immersion lithography, a resist pattern that exhibits high resolution and an excellent depth of focus can be inexpensively formed using the lens provided in an existing system. For example, JP 2008-133312 A and JP 2009-031767 A disclose a resist composition used for liquid immersion lithography.